9. Alkenes and Alkynes

When 2,2-dibromo-1-phenylpropane is heated overnight in fused KOH at 200 C, the major product is a foul-smelling compound of formula C₉H₈. Propose a structure for this product, and give a mechanism to account for its formation.

Problem-Solving Hint:

When 2,2-dibromo-1-phenylpropane is heated overnight with sodium amide at 150°C, the major product (after addition of water) is a different foul-smelling compound of formula C₉H₈. Propose a structure for this product, and give a mechanism to account for its formation.

An alternate method for the synthesis of alkynes relies on the double elimination of H―Br from a dihaloalkane under basic conditions. Suggest a mechanism for this reaction that we discuss in Chapter 12.

Show how you would accomplish the following synthetic transformations. Show all intermediates.

a. 2,2-dibromobutane → but-1-yne

When a double bond joins two carbon atoms, $\mathrm{isomers}$ can form.